In an engine turbocharger, for example, of the type shown in U.S. Pat. No. 4,719,818 for use on a turbocharged two stroke cycle medium speed diesel engine, particularly of the railway locomotive type, a rotor is provided including a stubshaft with integral drive gear, a turbine shaft with integral turbine wheel (which may have detachable blades) and a compressor impeller wheel drivingly attached to an end of the turbine shaft to be driven thereby at high speeds. This arrangement is only one example of numerous applications of shaft driven wheels wherein a wheel is detachably mounted to a drive shaft for high speed rotation requiring balancing of the assembly and wherein retention of the balanced condition upon detachment and reassembly is of importance.
In prior arrangements similar to U.S. Pat. No. 4,719,818, an impeller wheel, made of aluminum for light weight, is formed on a steel sleeve having internal splines. The splines are engaged with a close fit with mating splines at the end of a turbine shaft which drives the impeller wheel. The wheel is held in a fixed position on the shaft by a nut engaging a washer that forces the splined sleeve against an annular spacer which in turn is forced against a shoulder on the turbine shaft or drive shaft.
The turbine shaft and stubshaft assembly (rotor) is rotatably supported upon installation in a turbocharger on bearings engaging bearing journals between the impeller wheel and turbine wheel and between the turbine wheel and the stubshaft gear.
Prior to installation, the rotatable assembly (rotor) is assembled and dynamically balanced by adding or removing weight from selected portions of the rotor as required. However, when the rotor is again disassembled for installation in the turbocharger or, later, for inspection or service of the rotor on its bearings, the reassembly of the components may result in a substantial change in the balance of the assembly. This is thought to occur as a result of the necessary clearance between the splines of the drive shaft and sleeve which allows for some movement of the impeller wheel on the shaft prior to tightening of the nut, with the result that the impeller may be assembled in a slightly displaced position on the shaft each time it is reassembled. For this and other reasons, improved means for centering and retaining the impeller wheel on the drive shaft were desired.